Simple Math Question.

Downs

Hi,

How do you get the BASIC STAMP 2 to multiply a value with 48.92? I tried using Value1 */ $48EB but that's not correct. 48 being the upper byte and Taking .92 * 256 = 235 = ($EB) for the lower byte. I'm lost somewhere! Any help would be greatly appreciated. Thank you.

Downs

Never mind, figured it out. Thanks anyway!

davejames

Pray tell - what's the method?

Thanks,

DJ

Zoot

If you are multiplying by a fraction greater than 1, you get the Word value for the "mid-multiply" like this:

x * 5.2

= x */ ( 5.2 * 256 )
= x */ 1331 (decimal) or

result = x */ $533

Basically, for a mid-multiply, 5.2 = ( 5 * 256 ) + ( .2 * 256 )

If you are multiplying by a fraction less than 1, high-multiply gives more precision. It's basically the same thing but with $FFFF (65535 decimal):

x * .2
= x ** ( .2 * 65535 )
= x ** 13107 (decimal)

result = x ** $3333

Neither of these simple examples takes into account rounding... a better explicit mid-multiply might go something like this:

x * 5.2
= x */ (5.2 * 256)

result = ( (x * $533) + 128 ) / 256

Which takes into account rounding during the divide by 256 (mid-multiply does the exact same thing as above in 32bit math space, but doesn't add the 128 for rounding).

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Post Edited (Zoot) : 1/13/2009 11:08:24 PM GMT

davejames

Thanks Zoot.

DJ